1. Field of the Invention
The present invention relates to a shift system for use with a vehicular automatic transmission and, more particularly, to a shift system capable of switching between shift range change in an automatic mode and manual speed selection.
2. Description of the Prior Art
A shifter in a conventional automatic transmission has an I-shaped shift pattern, in which not only the individual ranges of parking (abbreviated hereinafter as "P"), reverse ("R"), neutral ("N") and drive ("D") ranges but also a second range (abbreviated hereinafter as "S") and a low range ("L") as modes for engine braking in uphill running are arranged in series.
The conventional automatic transmission is constructed to effect speed changes by a combination of two modes: the range change for determining each of the P, R, N, D, S and L ranges by mechanically switching the manual valve in a hydraulic servo control circuit for actuating the frictional engagement elements thereof; and the speed change for selecting a predetermined gear stage in the determined range by controlling the solenoid valves in the hydraulic servo control circuit electronically in accordance with the running speed and throttle opening of the vehicle. In the D, S and L ranges in the running mode, moreover, the speed changes in each range are automatically effected.
In order to enhance the fun of driving and the "feeling" of shifting a shift system has recently been introduced in the form of an automatic transmission to which is added a manual speed selecting mechanism enabling manual selection of a specific gear stage, reflecting the intention to give a driver positive control of shifting in forward running.
This shift system is exemplified by the technology which is disclosed in Japanese Patent Laid-Open No. 8545/1990. In this system, the automatic shift is carried out as in the prior art by moving the shift lever in a first shift pattern in an ordinary I pattern, and the manual speed charge is carried out by switching the shift lever sideways to a second shift pattern parallel to the first shift pattern and then moving it within the second shift pattern. In this system, moreover, the movement of the shift lever in the first shift pattern is mechanically transmitted to the transmission, and the movement of the shift lever in the second shift passage is detected by a sensor or switch which signals position of the shift lever and provides for electronic control of the transmission.
In the shift system described above, however, no means is provided for restricting and holding a linkage member, which is used for transmitting the motion of the shift lever in the first shift pattern to the transmission, in an uncoupled position, when the coupling between the shift lever and the linkage member is released by the transverse movement of the shift lever. As a result, the re-coupling of the shift lever when returned to the first shift pattern may lack smoothness due to misalignment.